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Information

Your software release
may not support all the features documented in this module. For the latest
caveats and feature information, see
Bug Search Tool and the
release notes for your platform and software release. To find information about
the features documented in this module, and to see a list of the releases in
which each feature is supported, see the feature information table.

Use Cisco Feature
Navigator to find information about platform support and Cisco software image
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Prerequisites for MPLS VPN CSC with LDP and IGP

The backbone carrier must enable the PE router to check that the packets it receives from the customer edge (CE) router contain only the labels that the PE router advertised to the CE router. This prevents data spoofing, which occurs when a packet from an unrecognized IP address is sent to a router.

Restrictions for MPLS VPN CSC with LDP and IGP

The following features are not supported with this feature:

ATM MPLS

Carrier supporting carrier traffic engineering

Carrier supporting carrier quality of service (QoS)

RSVP aggregation

VPN Multicast between the customer carrier and the backbone carrier network

The following router platforms are supported on the edge of the MPLS VPN:

Cisco 7200 series

Cisco 7500 series

Cisco 12000 series

See the table below for Cisco 12000 series line card support added for Cisco IOS releases.

Table 1 Cisco12000 Series Line Card Support Added for Cisco IOS Releases

Type

Line Cards

Cisco IOS Release Added

Packet over SONET (POS)

4-Port OC-3 POS

1-Port OC-12 POS

8-Port OC-3 POS

16-Port OC-3 POS

4-Port OC-12 POS

1-Port OC-48 POS

4-Port OC-3 POS ISE

8-Port OC-3 POS ISE

16 x OC-3 POS ISE

4 Port OC-12 POS ISE

1-Port OC-48 POS ISE

12.0(16)ST

12.0(21)ST

12.0(22)S

Electrical Interface

6- Port DS3

12- Port DS3

6-Port E3

12.0(16)ST

12.0(21)ST

ATM

4-Port OC-3 ATM

1-Port OC12 ATM

4-Port OC-12 ATM

12.0(22)S

Channelized Interface

2-Port CHOC-3

6-Port Ch T3 (DS1)

1-Port CHOC-12 (DS3)

1-Port CHOC-12 (OC-3)

4-Port CHOC-12 ISE

1-Port CHOC-48 ISE

12.0(22)S

Information About MPLS VPN CSC with LDP and IGP

MPLS VPN CSC Introduction

Carrier supporting carrier is where one service provider allows another service provider to use a segment of its backbone network. The service provider that provides the segment of the backbone network to the other provider is called the backbone carrier. The service provider that uses the segment of the backbone network is called the customer carrier.

Benefits of Implementing MPLS VPN CSC

The MPLS VPN CSC network provides the following benefits to service providers who are backbone carriers and to customer carriers.

Benefits to the Backbone Carrier

The backbone carrier can accommodate many customer carriers and give them access to its backbone. The backbone carrier does not need to create and maintain separate backbones for its customer carriers. Using one backbone network to support multiple customer carriers simplifies the backbone carrier’s VPN operations. The backbone carrier uses a consistent method for managing and maintaining the backbone network. This is also cheaper and more efficient than maintaining separate backbones.

The MPLS VPN carrier supporting carrier feature is scalable. Carrier supporting carrier can change the VPN to meet changing bandwidth and connectivity needs. The feature can accommodate unplanned growth and changes. The carrier supporting carrier feature enables tens of thousands of VPNs to be set up over the same network, and it allows a service provider to offer both VPN and Internet services.

The MPLS VPN carrier supporting carrier feature is a flexible solution. The backbone carrier can accommodate many types of customer carriers. The backbone carrier can accept customer carriers who are ISPs or VPN service providers or both. The backbone carrier can accommodate customer carriers that require security and various bandwidths.

Benefits to the Customer Carriers

The MPLS VPN carrier supporting carrier feature removes from the customer carrier the burden of configuring, operating, and maintaining its own backbone. The customer carrier uses the backbone network of a backbone carrier, but the backbone carrier is responsible for network maintenance and operation.

Customer carriers who use the VPN services provided by the backbone carrier receive the same level of security that Frame Relay or ATM-based VPNs provide. Customer carriers can also use IPSec in their VPNs for a higher level of security; it is completely transparent to the backbone carrier.

Customer carriers can use any link layer technology (SONET, DSL, Frame Relay, and so on) to connect the CE routers to the PE routers and the PE routers to the P routers. The MPLS VPN carrier supporting carrier feature is link layer independent. The CE routers and PE routers use IP to communicate, and the backbone carrier uses MPLS.

The customer carrier can use any addressing scheme and still be supported by a backbone carrier. The customer address space and routing information are independent of the address space and routing information of other customer carriers or the backbone provider.

Configuration Options for MPLS VPN CSC with LDP and IGP

The backbone carrier offers BGP and MPLS VPN services. The customer carrier can be one of the two types of service providers described in the following sections, which explain how the backbone and customer carriers distribute IPv4 routes and MPLS labels.

Customer Carrier Is an ISP

This section explains how a BGP/MPLS VPN service provider (backbone carrier) can provide a segment of its backbone network to a customer who is an ISP.

Consider the following example:

An ISP has two sites: one in California, the other in Maine. Each site is a point of presence (POP). The ISP wants to connect these sites using a VPN service provided by a backbone carrier. The figure below illustrates this situation.

Figure 1. Sample BGP/MPLS Backbone Carrier Supporting an ISP

Note

The CE routers in the figures are CE routers to the backbone carrier. However, they are PE routers to the customer carrier.

In this example, only the backbone carrier uses MPLS. The customer carrier (ISP) uses only IP. As a result, the backbone carrier must carry all the Internet routes of the customer carrier, which could be as many as 100,000 routes. This poses a scalability problem for the backbone carrier. To solve the scalability problem, the backbone carrier is configured as follows:

The backbone carrier allows only internal routes of the customer carrier (IGP routes) to be exchanged between the CE routers of the customer carrier and the PE routers of the backbone carrier.

MPLS is enabled on the interface between the CE router of the customer carrier and the PE router of the backbone carrier.

Internal and external routes are differentiated this way:

Internal routes go to any of the routers within the ISP.

External routes go to the Internet.

The number of internal routes is much lower than the number of external routes. Restricting the routes between the CE routers of the customer carrier and the PE routers of the backbone carrier significantly reduces the number of routes that the PE router needs to maintain.

Because the PE routers do not have to carry external routes in the VRF routing table, they can use the incoming label in the packet to forward the customer carrier Internet traffic. Adding MPLS to the routers provides a consistent method of transporting packets from the customer carrier to the backbone carrier. MPLS allows the exchange of an MPLS label between the PE and the CE routers for every internal customer carrier route. The routers in the customer carrier have all the external routes either through internal Border Gateway Protocol (iBGP) or route redistribution to provide Internet connectivity. The figure below shows how information is exchanged when the network is configured in this manner.

Figure 2. Backbone Carrier Exchanging Routing Information with a Customer Carrier Who Is an ISP

In the figure below, routes are created between the backbone carrier and the customer carrier sites. ASBR2 receives an Internet route that originated outside the network. All routers in the ISP sites have all the external routes through IBGP connections among them.

Figure 3. Establishing a Route Between a Backbone Carrier and a Customer Carrier Who Is an ISP

The table below describes the process of establishing the route, which can be divided into two distinct steps:

The backbone carrier propagates the IGP information of the customer carrier, which enables the customer carrier routers to reach all the customer carrier routers in the remote sites.

Once the routers of the customer carriers in different sites are reachable, external routes can be propagated in the customer carrier sites, using IBGP without using the backbone carrier routers.

Table 2 Establishing a Route Between the Backbone Carrier and the Customer Carrier ISP

Step

Description

1

CSC-CE2 sends the internal routes within site 2 to CSC-PE2. The routes include the route to ASBR2.

2

CSC-PE2 sends the routing information for site 2 to CSC-PE1, using MPLS VPN processes. CSC-PE1 gets one label (called L3), which is associated with the route to the VPN-IP address for ASBR2. CSC-PE1 gets another label (called L2), which is associated with the route to CSC-PE2.

3

CSC-PE1 sends the routing information associated with internal routes from site 2 to CSC-CE1. CSC-PE1 also sends the label binding information. As a result, CSC-CE1 gets the route to ASBR2 with CSC-PE1 as the next hop. The label associated with that route is called L1.

4

CSC-CE1 distributes the routing information through site 1. Every router in site 1 gets a route for every internal destination in site 2. Therefore, every router in site 1 can reach routers in site 2 and learn external routes through IBGP.

5

ASBR2 receives an Internet route.

6

The IBGP sessions exchange the external routing information of the ISP, including a route to the Internet. Every router in site 1 knows a route to the Internet, with ASBR2 as the next hop of that route.

Customer Carrier Is a BGP MPLS VPN Service Provider

When a backbone carrier and the customer carrier both provide BGP/MPLS VPN services, the method of transporting data is different from when a customer carrier provides only ISP services. The following list highlights those differences:

When a customer carrier provides BGP/MPLS VPN services, its external routes are VPN-IPv4 routes. When a customer carrier is an ISP, its external routes are IP routes.

When a customer carrier provides BGP/MPLS VPN services, every site within the customer carrier must use MPLS. When a customer carrier is an ISP, the sites do not need to use MPLS.

The figure below shows how information is exchanged when MPLS VPN services reside on all customer carrier sites and on the backbone carrier.

Figure 4. Backbone Carrier Exchanging Information with a Customer Carrier Who Is an MPLS VPN Service Provider

In the example shown in the figure below, routes are created between the backbone carrier and the customer carrier sites.

Figure 5. Establishing a Route Between a Backbone Carrier and a Customer Carrier Who Is an MPLS VPN Service Provider

The table below describes the process of establishing the route.

Table 3 Establishing a Route Between the Backbone Carrier and Customer Carrier Site

Step

Description

1

CE2 sends all the internal routes within site 2 to CSC-PE2.

2

CSC-PE2 sends the routing information for site 2 to CSC-PE1, using MPLS VPN processes. CSC-PE1 gets one label (called L3), which is associated with the route to the VPN-IP address for PE2. CSC-PE1 gets another label (called L2), which is associated with the route to CSC-PE2.

3

CSC-PE1 sends the routing information associated with internal routes from site 2 to CSC-CE1. CSC-PE1 also sends the label binding information. As a result, CSC-CE1 gets the route to PE2 with CSC-PE1 as the next hop. The label associated with that route is called L1.

4

CE1 distributes the routing and labeling information through site 1. Every router in site 1 gets a route for every internal destination in site 2. Therefore, PE1 can establish an MP-IBGP session with PE2.

5

CE2 advertises the internal routes of MPLS VPN site 2 to PE2.

6

PE2 allocates labels for all the VPN routes (regular MPLS VPN functionality) and advertises the labels to PE1, using MP-IBGP.

7

PE1 can forward traffic from VPN site 1 that is destined for VPN site 2.

The
as-number argument indicates the number of an autonomous system that identifies the router to other BGP routers and tags the routing information passed along. Valid numbers are from 0 to 65535. Private autonomous system numbers that can be used in internal networks range from 64512 to 65535.

Step 4

no bgp default ipv4-unicast

Example:

Router(config-router)# no bgp default ipv4-unicast

(Optional) Disables the IPv4 unicast address family on all neighbors.

Use the
no bgp default-unicast command if you are using this neighbor for MPLS routes only.

Step 5

neighbor {ip-address |
peer-group-name}
remote-asas-number

Example:

Router(config-router)# neighbor 10.5.5.5 remote-as 100

Adds an entry to the BGP or multiprotocol BGP neighbor table.

The
ip-address argument specifies the IP address of the neighbor.

The
peer-group-name argument specifies the name of a BGP peer group.

The
as-number argument specifies the autonomous system to which the neighbor belongs.

Step 6

neighbor {ip-address |
peer-group-name}
update-sourceinterface-type

Example:

Router(config-router)# neighbor 10.2.0.0 update-source loopback0

Allows BGP sessions to use a specific operational interface for TCP connections.

The
ip-address argument specifies the IP address of the BGP-speaking neighbor.

The
peer-group-name argument specifies the name of a BGP peer group.

The
interface-type argument specifies the interface to be used as the source.

Step 7

address-family vpnv4 [unicast]

Example:

Router(config-router)# address-family vpnv4

Enters address family configuration mode for configuring routing sessions, such as BGP, that use standard VPNv4 address prefixes.

Specifies that a communities attribute should be sent to a BGP neighbor.

The
ip-address argument specifies the IP address of the BGP-speaking neighbor.

The
peer-group-name argument specifies the name of a BGP peer group.

Step 9

neighbor {ip-address |
peer-group-name}
activate

Example:

Router(config-router-af)# neighbor 10.4.0.0 activate

Enables the exchange of information with a neighboring BGP router.

The
ip-address argument specifies the IP address of the neighbor.

The
peer-group-name argument specifies the name of a BGP peer group.

Step 10

end

Example:

Router(config-router-af)# end

(Optional) Exits to privileged EXEC mode.

Troubleshooting Tips

You can enter a
show ip bgp neighbor command to verify that the neighbors are up and running. If this command generates an error message, enter a
debug ip bgpx.x.x.xevents command, where
x.x.x.x is the IP address of the neighbor.

Configuring the CSC-PE and CSC-CE Routers

To enable the CSC-PE and CSC-CE routers to distribute routes and MPLS labels, perform the following tasks:

Prerequisites

Before you configure the CSC-PE and CSC-CE routers, you must configure an IGP on the CSC-PE and CSC-CE routers. A routing protocol is required between the PE and CE routers that connect the backbone carrier to the customer carrier. The routing protocol enables the customer carrier to exchange IGP routing information with the backbone carrier. Use the same routing protocol that the customer carrier uses. You can choose RIP, OSPF, or static routing as the routing protocol. BGP is not supported. For the configuration steps, see
Configuring MPLS Layer 3 VPNs
.

Configuring LDP on the CSC-PE and CSC-CE Routers

MPLS LDP is required between the PE and CE routers that connect the backbone carrier to the customer carrier. You can configure LDP as the default label distribution protocol for the entire router or just for the PE-to-CE interface for VRF.

SUMMARY STEPS

1.enable

2.configure terminal

3.mpls label protocol ldp

4.interfacetypenumber

5.mpls label protocol ldp

6.exit

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

mpls label protocol ldp

Example:

Router(config)# mpls label protocol ldp

Specifies MPLS LDP as the default label distribution protocol for the router.

The
number argument specifies the port, connector, or interface card number.

Step 5

mpls label protocol ldp

Example:

Router(config-if)# mpls label protocol ldp

(Optional) Specifies MPLS LDP as the default label distribution protocol for the interface.

Step 6

exit

Example:

Router(config-if)# exit

(Optional) Exits to privileged EXEC mode.

Enabling MPLS Encapsulation on the CSC-PE and CSC-CE Routers

Every packet that crosses the backbone carrier must be encapsulated, so that the packet includes MPLS labels. You can enable MPLS encapsulation for the entire router or just on the interface of the PE or CE router. To enable the encapsulation of packets, perform the following task.

The
number argument specifies the port, connector, or interface card number.

Step 5

mpls ip

Example:

Router(config-if)# mpls ip

(Optional) Enables MPLS encapsulation for the specified interface.

Step 6

exit

Example:

Router(config-if)# exit

(Optional) Exits to privileged EXEC mode.

Verifying the Carrier Supporting Carrier Configuration

The following commands verify the status of LDP sessions that were configured between the backbone carrier and customer carrier. Now the customer carrier ISP sites appear as a VPN customer to the backbone carrier.

SUMMARY STEPS

1.show mpls ldp discovery vrfvrf-name

2.show mpls ldp discovery all

DETAILED STEPS

Step 1

show mpls ldp discovery vrfvrf-name

Use this command to show that the LDP sessions are in VRF VPN1 of the PE router of the backbone carrier, for example:

MPLS VPN CSC Network with a Customer Who Is an ISP Example

The figure below shows a carrier supporting carrier network configuration where the customer carrier is an ISP. The customer carrier has two sites, each of which is a POP. The customer carrier connects these sites using a VPN service provided by the backbone carrier. The backbone carrier uses MPLS. The ISP sites use IP. To enable packet transfer between the ISP sites and the backbone carrier, the CE routers that connect the ISPs to the backbone carrier run MPLS.

Figure 6. Carrier Supporting Carrier Network with a Customer Carrier Who Is an ISP

The following examples show the configuration of each router in the carrier supporting carrier network. OSPF is used to connect the customer carrier to the backbone carrier.

MPLS VPN CSC Network with a Customer Who Is an MPLS VPN Provider Example

The figure below shows a carrier supporting carrier network configuration where the customer carrier is an MPLS VPN provider. The customer carrier has two sites. The backbone carrier and the customer carrier use MPLS. The IBGP sessions exchange the external routing information of the ISP.

Figure 7. Carrier Supporting Carrier Network with a Customer Carrier Who Is an MPLS VPN Provider

The following configuration examples show the configuration of each router in the carrier supporting carrier network. OSPF is the protocol used to connect the customer carrier to the backbone carrier.

Additional References for MPLS VPN Carrier Supporting Carrier Using LDP and an IGP

Related Documents

RFCs

RFC

Title

RFC 2547

BGP/MPLS VPNs

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online
resources to download documentation, software, and tools. Use these
resources to install and configure the software and to troubleshoot
and resolve technical issues with Cisco products and technologies.
Access to most tools on the Cisco Support and Documentation website
requires a Cisco.com user ID and password

Feature Information for MPLS VPN CSC with LDP and IGP

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Table 4 Feature Information for MPLS VPN CSC with LDP and IGP

Feature Name

Releases

Feature Configuration Information

MPLS VPN Carrier Supporting Carrier

12.0(14)ST

12.0(16)ST

12.2(8)T

12.0(21)ST

12.0(22)S

12.0(23)S

Cisco IOS XE Release 2.2

This feature enables you to set up and create an MPLS VPN CSC network that uses LDP to transport MPLS labels and an IGP to transport routes.

In 12.0(14)ST, this feature was introduced.

In 12.0(16)ST, this feature was integrated.

In 12.2(8)T, this feature was integrated.

In 12.0(21)ST, this feature was integrated.

In 12.0(22)S, this feature was integrated.

In 12.0(23)S, this feature was integrated.

In Cisco IOS XE Release 2.2, this feature was implemented on the Cisco ASR 1000 Series Routers.

This feature uses no new or modified commands.

Glossary

ASBR-- Autonomous System Boundary router. A router that connects one autonomous system to another.

autonomous system--A collection of networks under a common administration sharing a common routing strategy.

BGP--Border Gateway Protocol. An interdomain routing protocol that exchanges network reachability information with other BGP systems (which may be within the same autonomous system or between multiple autonomous systems).

CE router--customer edge router. A router that is part of a customer network and that interfaces to a provider edge (PE) router. CE routers do not recognize associated MPLS VPNs.

CSC--Carrier Supporting Carrier. A hierarchical VPN model that allows small service providers, or customer carriers, to interconnect their IP or MPLS networks over an MPLS backbone. This eliminates the need for customer carriers to build and maintain their own MPLS backbone.

eBGP--external Border Gateway Protocol. A BGP between routers located within different autonomous systems. When two routers, located in different autonomous systems, are more than one hop away from one another, the eBGP session between the two routers is considered a multihop BGP.

edge router--A router that is at the edge of the network. It defines the boundary of the MPLS network. It receives and transmits packets. Also referred to as edge label switch router and label edge router.

iBGP--internal Border Gateway Protocol. A BGP between routers within the same autonomous system.

IGP--Interior Gateway Protocol. Internet protocol used to exchange routing information within a single autonomous system. Examples of common Internet IGP protocols include IGRP, OSPF, IS-IS, and RIP.

MPLS--Multiprotocol Label Switching. The name of the IETF working group responsible for label switching, and the name of the label switching approach it has standardized.

NLRI--Network Layer Reachability Information. The BGP sends routing update messages containing NLRI to describe a route and how to get there. In this context, an NLRI is a prefix. A BGP update message carries one or more NLRI prefixes and the attributes of a route for the NLRI prefixes; the route attributes include a BGP next hop gateway address and extended community values.

NSF--Nonstop forwarding enables routers to continuously forward IP packets following a Route Processor takeover or switchover to another Route Processor. NSF maintains and updates Layer 3 routing and forwarding information in the backup Route Processor to ensure that IP packets and routing protocol information are forwarded continuously during the switchover and route convergence process.

PE router--provider edge router. A router that is part of a service provider’s network. It is connected to a customer edge (CE) router. All MPLS VPN processing occurs in the PE router.

QoS--quality of service. Measure of performance for a transmission system that indicates its transmission quality and service availability.

RD--route distinguisher. An 8-byte value that is concatenated with an IPv4 prefix to create a unique VPN-IPv4 prefix.

RT--route target. Extended community attribute used to identify the VRF routing table into which a prefix is imported.

SLA--Service Level Agreement given to VPN subscribers.

VPN--Virtual Private Network. A secure MPLS-based network that shares resources on one or more physical networks (typically implemented by one or more service providers). A VPN contains geographically dispersed sites that can communicate securely over a shared backbone network.

VRF--VPN routing and forwarding instance. Routing information that defines a VPN site that is attached to a PE router. A VRF consists of an IP routing table, a derived forwarding table, a set of interfaces that use the forwarding table, and a set of rules and routing protocols that determine what goes into the forwarding table.